void CClockShow::OnPaint() 
{
    CPaintDC dc(this);
    CDC *pDC = new CDC;
    pDC->CreateCompatibleDC(&dc);

    CRect rc;
    GetClientRect(&rc);

    pDC->MoveTo(0,0);
    pDC->LineTo(10,10);
          dc.BitBlt((rc.Width()-20)/2,0,rc.right-rc.left,rc.bottom-rc.top,pDC,0,0,
                          SRCCOPY);

}
为什么这样没有显示啊？